Subject: initialization of std::string_view with null pointer (#61)
Subject: initialization of std::string_view with null pointer (#61)

When switching to C++17, absl::string_view implicitly uses
std::string_view. Initialization of string_view with nullptr was
allowed in abseil implementation of string_view but the same is not
true in std. https://github.com/google/cel-cpp/pull/45 fixes majority
of these instances. But, in this instance, it has been left out.

Signed-off-by: Yifan Yang <c2f26873f6f1dbfd1f69cf1310e6a5b9b51d612b@google.com>

Co-authored-by: Yifan Yang <c2f26873f6f1dbfd1f69cf1310e6a5b9b51d612b@google.com>
google/cel-cpp,google/cel-cpp